Embodiments described herein relate generally to multiple-input-multiple-output (MIMO) data transmission and more particularly, to apparatus and methods of use for an antenna system with multi-polarization.
In some instances, the performance of a radio and/or the performance of a wireless link using a multi-stream Institute of Electrical and Electronics Engineers (IEEE) 802.11(a/b/g/n/ac) MIMO protocol can be dependent on the ability of the radio to isolate and differentiate between multiple data streams. As such, one or more antenna techniques can be implemented to enhance the antenna diversity (i.e., to isolate and differentiate multiple data streams). Such antenna techniques can include, for example, spatial diversity, pattern diversity, polarity diversity, and/or the like. Specifically, spatial diversity employs multiple antennas, generally with the same characteristic, that are physically separated from one another by a distance on the order of the signal wavelength to multiple miles. Pattern diversity employs multiple directive antennas that are co-located (e.g., within a relatively short distance of about the signal wavelength or less) with different radiation patterns to provide a higher gain versus a single omnidirectional antenna. Polarity diversity typically combines pairs of cross-polarized antennas (i.e., antennas with orthogonal polarizations, such as horizontal and vertical, +slant 45° and −slant 45°, etc.) to immunize a system from polarization mismatches that would potentially otherwise cause signal fade.
Often, in buildings (e.g., homes, offices, etc.) when no clear line-of-sight (LOS) exists between a transmitter and a receiver, a signal can be reflected along multiple paths before finally being received. In such scenarios, multiple antennas at the receiver can provide several observations of the same signal that are received via the multiple paths. In some instances, each antenna can experience a different interference environment along the corresponding path. Thus, if one antenna is experiencing a deep fade, another antenna likely has a sufficient signal. Collectively, such a system can provide a robust wireless link. Similarly, multiple antennas can be proven valuable for transmitting systems as well as the receiving systems. As a result, antenna diversity at the transmitter and/or the receiver can be effective at mitigating the multipath situations and providing an overall good performance for the wireless link.
In settings without high multipath ability, however, systems employing MIMO often exhibit reduced signal performance. For example, in large campus settings and/or the like with limited surfaces to reflect the signal (e.g., in instances of LOS transmission, and/or the like), signal diversity can be limited due, at least in part, to the LOS component of the signal overwhelming the multipath components of the signal. In this manner, a larger importance can be placed on polarization diversity to achieve the desired signal diversity. Radios, however, often include orthogonal antennas having only two polarizations (e.g., horizontal and vertical), which can still result in limited signal diversity.
Thus, a need exists for methods and apparatus for multi-polarization antenna systems.